Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit cell) of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
Battery cells constituting such a middle or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. In particular, the laminate sheet of each pouch-shaped battery widely used in the battery module has a polymer material exhibiting low thermal conductivity coated on the surface thereof with the result that it is difficult to effectively lower the overall temperature of the battery cells.
If the heat, generated from the battery module during the charge and discharge of the battery module, is not effectively removed from the battery module, the heat accumulates in the battery module with the result that deterioration of the battery module is accelerated. According to circumstances, the battery module may catch fire or explode. For this reason, a cooling system is needed in a middle or large-sized battery pack for vehicles, which is a high-power, large-capacity battery including a plurality of middle or large-sized battery modules, to cool battery cells mounted in the battery pack.
Each battery module mounted in a middle or large-sized battery pack is generally manufactured by stacking a plurality of battery cells with high integration. In this case, the battery cells are stacked in a state in which the battery cells are arranged at predetermined intervals so that heat generated during the charge and discharge of the battery cells is removed. For example, the battery cells may be sequentially stacked in a state in which the battery cells are arranged at predetermined intervals without using an additional member. Alternatively, in a case in which the battery cells have low mechanical strength, one or more battery cells are mounted in a battery cartridge, and a plurality of battery cartridges is stacked to constitute a battery module. Coolant channels may be defined between the stacked battery cells or between the stacked battery modules so that heat accumulating between the stacked battery cells or between the stacked battery modules is effectively removed.
In this structure, however, it is necessary to provide a plurality of coolant channels corresponding to the number of the battery cells with the result that the overall size of the battery pack is increased.
In particular, in a case in which the cooling structure is based on a water cooling type cooling system, a plurality of coolant channels is defined between the battery cells or between the battery modules with the result that it is very difficult to design the cooling structure. In addition, if a cooling member is mounted to a specific region of the batter pack to constitute the cooling structure, overall size of the battery pack is increased.
Also, in a case in which the cooling structure is based on an air cooling type cooling system, intervals of the coolant channels are relatively narrowed, when a plurality of battery cells or battery modules is stacked, in consideration of the size of the battery pack. As a result, design of the cooling structure is complicated. That is, high pressure loss is caused by the coolant channels arranged at intervals narrower than a coolant inlet port with the result that it is difficult to design shapes and positions of the coolant inlet port and a coolant outlet port. Also, a fan may be further provided to prevent such pressure loss, and therefore, design may be restricted due to power consumption, fan noise, space or the like.
Furthermore, in a case in which the cooling structure is based on an air cooling type cooling system, coolant channels are provided at the upper and lower parts of the battery pack to constitute a coolant introduction part and a coolant discharge part so that a coolant is introduced from the coolant introduction part to cool the respective battery modules and is then discharged to the coolant discharge part with the result that overall size of the battery pack is increased.
Consequently, there is a high necessity for a battery pack which provides high-power, large-capacity electricity, which can be manufactured in a simple and compact structure, and which exhibits excellent cooling efficiency and safety.